1. Field of the Invention
The invention concerns a system for attaching two rotating parts made of materials having different expansion coefficients, and more particularly to the attachment of an inner exhaust cap on the exhaust housing of a turbojet.
2. Description of the Prior Art
The current trend in the aeronautics industry is in the direction of reducing the weight of airframes and engines by using low-density composite materials. This reduction in weight leads to a reduction in fuel comsumption and an increase in the load carried. Weapons-equipped aircraft make use of these materials, especially for airfoil and airframe elements. In contrast, their use in engines has not been very widespread because of the difficulties of using them in association with classic materials having relatively high expansion coefficients.
French Pat. No. 2,408,037, for example, describes the connection of a swivelling nozzle of woven carbon to an exhaust structure. The nozzle is girdled by rings of refractory cement. One of the rings is attached to the structure by flexible stops and the other is attached to the steering actuators by means of a metal box. The fact that the nozzle is connected by movable and flexible parts to the exhaust duct allows free axial as well as radial expansion of the latter without subjecting the woven carbon part to unacceptable stress.
Attempts have been made to replace other engine elements with composite material parts, in particular the inner exhaust cap or cone which is an extension of the exhaust housing. Tests have shown that it was not possible to connect the cap to the housing by known systems, as for example, the system disclosed in French Patent 1,458,204 for mounting a heat-protection sleeve in a post-combustion chamber. The screw-and-slipper system used does allow axial expansion but does not accept radial expansion very well. This system is usable only for metal materials having significant elongations.